The top five spam subjects sullying inboxes

Security biz Websense has drawn up a list of the five most common spam subject lines.

The nuisance list, based on the subject lines of the millions of spam messages blocked by the firm every day, highlights the danger of opening attachments or clicking dodgy links. The most commonly seen subject lines fall into the one of the five categories listed below:

Bogus online orders - For example, "Order N21560", although the numbers vary. These pose as Adobe CS4 licences but actually redirect to sites serving up the Blackhole exploit kit.

Fake fines - "FW: Re: UNIFORM TRAFFIC TICKET (ID: 239127922)", numbers vary and subject might appear without FW: or RE:, or "Fwd: Your Flight Order N125-9487755", again numbers vary. Users are lured to click on a link, which redirects to another malicious site serving the Blackhole exploit kit.

Package delivery lies- For example, "USPS Invoice copy ID46298", "FedEx: New Agent File Form, trackid: 1V6ZFZ7FEOHUQ" or "DHL Express Notification for shipment 90176712199". As before, numbers vary between different spam messages. "Fake emails pretending to be invoices or tracking emails have been around for several years and usually would have an attachment, such as a Trojan like Zeus or SpyEye," Websense reports. Malicious emails of this type are still been sent out in bulk, using attachments that are repackaged for every campaign, as a tactic designed to get around antivirus defences.

Tests for working addresses - These often appear under the guise of a patch for World of Warcraft. "Unfortunately, for the criminals, the archive is corrupt and therefore harmless to the recipients," Websense reports, though other campaigns using the same subject line do appear with working malicious code attached. In other cases the subject line is used by spammers to validate email addresses as active.

Payment and tax cons - For example "FRAUD ALERT for ACH", "Your Wire Transfer", "IRS requires new EIN", and "IRS Tax report". Many spam-bots spewing this type of email are misconfigured so that they automatically send out dodgy emails with an August date stamp, even though we are now reaching towards the end of November.

Websense adds that spam slurries normally follow the pattern of running for only about an hour or less before disappearing for a while, sometimes only to return with another short-lived tsunami of email crud.

Miscreants often switch between attachments and using links to malicious or compromised websites to distribute malware. Repackaging attachments so they will not be detected automatically by antivirus scanners is also commonplace. Changing the template of spam emails is also extremely commonplace.

A blogpost by Websense on spam subject lines and associated tactics, which features a rogues' gallery of dodgy emails, can be found here. ®